TFI-OFDM transmission/reception systems for UWB communication and methods thereof for mitigating interference from simultaneously operating piconets

ABSTRACT

A TFI-OFDM transmission system includes a data generator generating data having a speed corresponding to a transmission speed mode; a convolutional encoder convolutional-encoding the data, an interleaver bit-interleaving the encoded data, an OFDM modulator inputting a first data group into a positive frequency domain and a second data group into a negative frequency domain, executing an IFFT, and outputting OFDM symbols; a buffer temporarily storing the OFDM symbols in order to sequentially transmit the OFDM symbols in a time domain at least two times; and a frequency generator generating certain frequencies to transmit the OFDM symbols in a certain number of frequency bands corresponding to transmission channels.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/486,414, filed on Jul. 14, 2003 in the United States Patent andTrademark Office, and Korean Patent Application No. 2004-21276, filed onMar. 29, 2004 in the Korean Patent Office, the disclosures of which areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to TFI-OFDM transmission and receptionsystems and methods thereof for mitigating interference from adjacentpiconets in multi-band orthogonal frequency division multiplexing forultra wide band (UWB) transmissions.

2. Description of the Related Art

In a wireless communication environment utilizing a wide frequency band,such as the ultra wide band (UWB) 3.1˜10.6 GHz, the entire frequencyband is divided into a single sub-band or a finite number of sub-bands.A continuous wave is not used in a time domain, of which signals existin every time domain, but rather, a form of a wave packet is used, ofwhich signals exist in a certain region of the time domain. In a singleband system that uses a single frequency band, an impulse utilizingevery frequency of the UWB is adopted for transmission and receivingsignals. However, the single band system tends to be vulnerable tointerference from other systems. To address his shortcoming, amulti-band system utilizes a plurality of sub-bands as the need arisesto effectively cope with the interference. However, when using a RFcircuit consisting of a single oscillator, the performance of themulti-band system may be seriously degraded since the energy finishedfrom the multi-path fading channel reaches about 20% of the entireenergy. To overcome this shortcoming, the Texas Instrument (TI) Co.suggested a time frequency interleaved-orthogonal frequency divisionmultiplexing (TFI-OFDM) system for the transmission scheme.

FIGS. 1A and 1B illustrate data spectrums in the frequency domain whichare transmitted according to the conventional TFI-OFDM transmissionscheme.

FIG. 1A illustrates a 55 Mbps mode of the transmission scheme, in whichonly a half (½) of the positive frequency domain carries actual data,and the remaining half (½) of the positive domain carries a copy of theactual data. The negative frequency domain carries a complex conjugateof the data in the positive domain. FIG. 1B illustrates 110 Mbps and 200Mbps modes, in which the positive frequency domain carries the actualdata and the negative frequency domain carries the complex conjugate ofthe actual data.

FIG. 2 illustrates a transmission scheme extended in the frequencydomain according to the conventional TFI-OFDM transmission system.Shortcomings of the conventional transmission system are described withreference to FIG. 2. Piconet A has a transmission channel {f₁, f₂, f₃,f₁, f₂, f₃, . . . } and piconet B has a transmission channel {f₃, f₂,f₁, f₃, f₂, f₁, . . . } by using three frequency bands f₁, f₂, f₃. Asshown in FIG. 2, piconets A and B collide with each other. For example,the OFDM symbol A2 of piconet A, which is transmitted in the frequencyband f₂, collides with the OFDM symbol B2 of piconet B. The collidedOFDM symbols cannot be recovered at a receiving side.

Accordingly, there is a need to mitigate the effect of collisionsresulting from adjacent simultaneously operating piconets (SOPs) in theconvention TFI-OFDM system.

SUMMARY OF THE INVENTION

To address the above and other shortcomings, an aspect of the presentinvention is to provide a TFI-OFDM transmission system and methodthereof for loading and transmitting different data in a positive and anegative frequency domain and applying a transmission scheme of timedomain extension, and another aspect is to provide a correspondingTFI-OFDM reception system and method thereof.

To achieve the above aspects of the present invention, the TFI-OFDMtransmission system includes a data generator generating data having aspeed corresponding to transmission speed mode; a convolutional encoderconvolutional-encoding the data; an interleaver bit-interleaving theencoded data; an OFDM modulator inputting a first data group into apositive frequency domain and a second data group into a negativefrequency domain, executing an IFFT, and outputting OFDM symbols; abuffer temporarily storing the OFDM symbols in order to sequentiallytransmit the OFDM symbols in a time domain at least two times; and afrequency generator generating certain frequencies to transmit the OFDMsymbols in a certain number of frequency bands corresponding totransmission channels.

Advantageously, the convolutional encoder has a ⅓ coding rate andoutputs first, second, and third data groups which are respectivelyencoded in fir second, and third generators. The interleaver executes atone-interleaving with respect to each of the first, second, and thirddata groups.

According to another aspect of the present invention, the TFI-OFDMtransmission method includes (a) generating data having a ratecorresponding to a transmission speed mode; (b) convolutional-encodingthe data; (c) bit-interleaving the encoded data; (d) inputting a firstdata group into a positive frequency domain and a second data group intoa negative frequency domain, executing an invert fast Fourier transform(IFFT), and outputting OFDM symbols; (e) sequentially transmitting theOFDM symbols in different frequency bands at least two times.

Advantageously, step (b) encodes at a ⅓ coding rate and outputs first,second, and third data groups. Step (c) executes a tone-interleaving toeach of the first, second, and third data groups.

The TFI-OFDM reception system includes a receiver receiving OFDM symbolstransmitted in a certain number of frequency bands corresponding totransmission channels, a collision detector determining collisions of atleast two OFDM symbols by measuring the powers with respect to at leasttwo OFDM symbols sequentially received and containing the same data, anda data detector detecting data to be processed based on collisioninformation which is determined with respect to the at least two OFDMsymbols by the collision detector.

The collision detector measures a first power and a second power withrespect to first OFDM symbols and second OFDM symbols which are the samedata sequentially received from a first frequency band and a secondfrequency band; measures a first average power and a second averagepower with respect to signals received from the first and secondfrequency bands; compares the first power and the first average power,compares the second power and the second average power, determineswhether there are collisions in the first OFDM symbols and second OFDMsymbols, and provides the information to the data detector.

According to yet another aspect of the present invention, the TFI-OFDMreception method includes (a) receiving OFDM symbols transmitted in acertain number of frequency bands corresponding to transmissionchannels; (b) determining collisions in at least two OFDM symbols bymeasuring the powers with respect to the at least two OFDM symbolssequentially received and containing the same data, and (c) detectingdata to be processed from the at least two OFDM symbols based on thecollision determination.

Step (b) includes (b-1) measuring a first power and a second power withrespect to a first OFDM symbols and a second OFDM symbols which are thesame data sequentially received from a first frequency band and a secondfrequency band; (b-2) measuring a first average power and a secondaverage power with respect to each signal received from the firstfrequency band and second frequency band; and (b-3) comparing the firstpower and the first average power, comparing the second power and thesecond average power, determining whether there are collisions in thefirst OFDM symbols and second OFDM symbols, and providing theinformation to step (c).

BRIEF DESCRIPTION OF THE DRAWING FIGURES

These and/or other aspects and advantages of the present invention willbe readily apparent and appreciated by describing in detail exemplaryembodiments thereof with reference to the accompanying drawings, inwhich:

FIGS. 1A and 1B are diagrams illustrating a spectrum in a frequencydomain of data transmitted in a conventional TFI-OFDM transmissionsystem;

FIG. 2 is a diagram illustrating a transmission scheme extended in thefrequency domain of the conventional TFI-OFDM system;

FIG. 3A is a schematic block diagram illustrating a TFI-OFDMtransmission system according to an embodiment of the present invention;

FIG. 3B is a schematic block diagram illustrating the TFI-OFDMtransmission system according an alternative embodiment of the presentinvention;

FIG. 4 is a conceptual diagram illustrating the transmission schemeaccording to an embodiment of the present invention;

FIG. 5 is a conceptual diagram illustrating inter-symbol collisions in amulti-piconet environment according to an embodiment of the presentinvention;

FIGS. 6A to 6C are diagrams illustrating the mission scheme according toan embodiment of the present invention;

FIGS. 7A to 7D are diagrams illustrating examples of the transmission onscheme applied to each of transmission channel patterns according to anembodiment of the present invention;

FIG. 8 is a schematic block diagram illustrating a TFI-OFDM receptionsystem corresponding to the transmission scheme according to anembodiment of the present invention; and

FIG. 9 is a flowchart illustrating exemplary steps for selectivelydetecting non-collided OFDM symbols in the multi-piconet environment bythe TFI-OFDM reception system according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF ILLUSTRATIVE, NON-LIMITING EMBODIMENTS OF THEINVENTION

The present invention will now be described more fully with reference tothe accompanying drawings, in which illustrative, non-limitingembodiments of the invention are shown. In the drawings, like referencenumbers refer to like elements throughout

Prior to describing the exemplary embodiments of the present invention,it is assumed that a time frequency interleaved-orthogonal frequencydivision multiplexing (TFI-OFDM) system utilizes a ⅓ convolutionalencoder, an applicable transmission speed mode is limited to 110 Mbpsand 200 Mbps, and a transmission band has three frequency bands f₁, f₂,f₃. It should be appreciated that the ⅓ convolutional encoder isexemplary for purposes of explanation and not limitation, as well as thetransmission speed.

FIG. 3A is a schematic block diagram illustrating the TFI-OFDMtransmission system according to an embodiment of the present invention.As shown in FIG. 3A, the transmission system includes a data generator310, a convolutional encoder 320, an interleaver 330, a quadrature phaseshifting keying (QPSK) modulator 340, an orthogonal frequency divisionmultiplexing (OFDM) modulator 350, a guard interval (GI) inserter 360, adigital-to-analog (D/A) converter 370, a buffer 380, and a frequencygenerator 390.

The data generator 310 generates binary data having a ratiocorresponding to transmission speed modes, for example, 10 Mbps and 200Mbps, which is defined in the system.

The convolutional encoder 320 convolutional-encodes an input data at acertain coding rate. For example, a 200 bit input data is output as 600bit coded data at a ⅓ coding rate.

The interleaver 330 performs symbol interleaving and tone interleavingto the coded data.

The QPSK modulator 340 QPSK-modulates the input data For instance, if200 bit data is input, the QPSK modulator 340 outputs 100 symbol data bymapping 2 bits into each symbol.

The OFDM modulator 350 modulates data of a frequency domain into OFDMsymbols of a time domain using an invert fast Fourier transform (IFFT).According to an embodiment of the present invention, the OFDM modulator350 outputs OFDM symbols in the form of a complex conjugate by inputtingdifferent data into the positive and negative frequency domains,respectively, and executing the IFFT. Hence, double the amount of dataare transmitted as compared with the OFDM symbols of the time domain inthe conventional TFI-OFDM transmission system.

The GI inserter 360 copies a certain interval of a rear part of theIFFT-executed OFDM symbols and inserts the certain interval into a frontpart of the OFDM symbol so as to maintain orthogonality of the OFDMsymbols in multi-path channel conditions. The certain interval insertedinto the front of the OFDM symbol is referred to as a guard interval(GP).

The D/A converter 370 converts a digital signal into an analog signal.

The buffer 380 temporarily stores the transmitted OFDM symbols andtransmits the same OFDM symbols in the time domain sequentially morethan two times, to thus extend the OFDM symbols into the time domain.

The frequency generator 390 generates frequencies corresponding to threefrequency bands in accordance with a pre-set transmission channelpattern. Thus, the OFDM symbols, which are converted to the final analogsignals, are up-converted sequentially into predetermined frequencybands.

Accordingly, in the TFI-OFDM transmission system according to anembodiment of the present invention, the OFDM symbols transmit doublethe data amount as compared with the conventional OFDM symbols, and thedata are sequentially transmitted two times in the different frequencybands depending on the transmission channel.

FIG. 3B is a schematic block diagram illustrating the TFI-OFDMtransmission system according an alternative embodiment of the presentinvention. Detailed description of like elements in the FIG. 3A areomitted for conciseness.

The transmission system includes a convolutional encoder 321, aninterleaver 331, a QPSK modulator 341, an OFDM modulator 351, a buffer381, and a frequency generator 391.

The convolutional encoder 321 has a ⅓ coding rate and, accordingly,includes thee generator polynomials (hereinafter refer to as first,second, and third generators). The first, second, and third generatorsG1, G2 and G3 each output the encoded data. If 200-bit data is input,the first, second, and third generators G1, G2, and G3 each outputs200-bit coded first, second, and third data groups, respectively.

The interleaver 331 omits the symbol interleaving and performs the toneinterleaving alone with respect to the fist, second, and third datagroups respectively output from the first, second, and third generatorsG1, G2, and G3 of the convolutional encoder 320.

The QPSK modulator 341 performs the QPSK modulation to thetone-interleaved first, second, and third data groups.

The OFDM modulator 351 modulates data of the frequency domain into OFDMsymbols of the time domain through the IFFT. According to an alternateembodiment of the present invention, the OFDM modulator 351 inputsdifferent data into the positive and the negative frequency domains,respectively, and executes the IFFT to the input data. The positivefrequency domain is input with the first data group, and the negativefrequency domain is input with the second data group. The IFFT-executedOFDM symbols correspond to the first and the second data groups.

Subsequently, a GI is inserted into the OFDM symbols and the OFDMsymbols are converted to an analog signal.

The buffer 381 temporarily stores the OFDM symbols to extend the OFDMsymbols into the time domain. Hence, the same OFDM symbols aresequentially transmitted in the time domain at least two times. Thefrequency generator 391 generates frequencies corresponding to the threefrequency bands f₁, f₂, f₃ in accordance with the predeterminedtransmission channel pattern

The final analog-converted OFDM symbols are sequentially up-convertedtwo times to a certain frequency band. For example, if the transmissionchannel is {f₁, f₂, f₃ f₁, f₂, f₃}, the final analog-converted OFDMsymbols are transmitted once in the frequency domain f₁ at the time T₀,temporarily stored in the buffer 380, and transmitted once again in thefrequency domain f₂ at the next time T₁.

The above descriptions are made with respect to the 110 Mbps and 200Mbps modes. As for a 55 Mbps mode, the OFDM modulator 350 or 351utilizes a different data input scheme. Specifically, a half (½) of thepositive frequency domain is input with actual first data, and theremaining half (½) of the positive frequency domain is input with thesame data which is the copy of the actual first data. Similarly, a half(½) of the negative frequency domain is input with actual second data,and the remaining half (½) of the negative frequency domain is inputwith the copy of the actual second data. These loaded data areIFFT-executed and output as the OFDM symbols having double the dataamount as compared with the conventional OFDM symbols of the 55 Mbps.Next, the OFDM symbols are data-processed and transmitted in the timedomain two times as mentioned above. Consequently, the same datatransmission rate is obtained as in the 55 Mbps mode. As for a 480 Mbpsmode, the conventional transmission scheme is applied.

FIG. 4 is a conceptual diagram illustrating the transmission schemeextended into the time domain of the TFI-OFDM transmission systemaccording to an embodiment of the present invention, which is describedin greater detail below. Byway of example, piconet A as described belowhas the transmission channel pattern {f₃, f₁, f₂, f₃, f₁, f₂} withrespect to the three frequency bands {f₁, f₂, f₃}.

As shown in FIG. 4, OFDM symbols loaded in each frequency band containdifferent data in the positive and negative frequency domains,respectively, and are transmitted two times along the time axis.Specifically, the OFDM symbols A11 and A12, which are initiallytransmitted in the frequency band f₃ at the time T₀, are transmittedonce again in the frequency band f₁ at the time T₁. In the same manner,a plurality of the OFDM symbols are transmitted two times in thefrequency bands according to the transmission channel pattern. Thetransmission scheme has the same data transmission rate as theconventional transmission scheme of FIG. 2 with respect to the OFDMsymbols transmitted at the times T₀ to T₅.

FIG. 5 is a conceptual diagram illustrating inter-symbol collisions in amulti-piconet environment according to an embodiment of the presentinvention, in which performances of adjacent simultaneously operatingpiconets (SOPs) are enhanced while the same data transmission rate ismaintained as in the conventional transmission scheme of FIG. 2.

Referring now to FIG. 5, the transmission channel pattern of piconet Ais {f₁, f₂, f₃, f₁, f₂, f₃} and that of piconet B is {f₃, f₂, f₁, f₃,f₂, f₁ . . . } with respect to the three frequency bands f₁, f₂, f₃. TheOFDM symbol A1 of piconet A, which is transmitted in the frequency bandf₂ at the time T₁, collides with the OFDM symbol B1 of piconet B. TheOFDM symbol A3 of piconet A, which is transmitted in the frequency bandf₂ at the time T₄, collides with the OFDM symbol B3 of piconet B.Accordingly, the inter-symbol collisions are inevitable due to theadjacent SOPs in the multi-piconets.

The transmission scheme extended to the time domain according to anembodiment of the present invention, transits the same OFDM symbol twotimes along the time axis so that the collided OFDM symbols A1, B1, A3,and B3 are re-transmitted in other frequency bands at the previous timeinterval or at the next time interval. As a result, even if an OFDMsymbol has collided and is lost, other OFDM symbols are losslesslytransmitted since the same OFDM symbols are transmitted two times sothat the adjacent SOP performance is definitely enhanced.

FIG. 6A to 6C are diagrams illustrating the transmission schemeaccording to an embodiment of the present invention.

FIG. 6A illustrates a case when each transmission channel CH#2, CH#3,and CH#4 is delayed for 0.5 OFDM symbol with respect to the transmissionchannel CH#1, which results in collisions between adjacent transmissionchannels. The transmission channel CH#2 has four symbol collisions withrespect to the transmission channel CH#1, and the transmission channelsCH#3 and CH#4 each have three symbol collisions with respect to thetransmission channel CH#1. Thus, the transmission channel CH#1experiences the worst channel conditions in the vicinity of thetransmission channel CH#2. Referring to FIG. 6B, only 400 bits of dataare losslessly transmitted with respect to the transmitted 600 bit data

If the transmission system of FIG. 3B data-processes the OFDM symbolsbeing transmitted in the transmission channel CH#1, the first OFDMsymbols transmitted in the frequency bands f₁ and f₂ correspond to thefirst data group output from the first generator G1 of the convolutionalencoder 321, second OFDM symbols transmitted in the frequency bands f₃and f₁ correspond to the second data group output from the secondgenerator G2, and third OFDM symbols transmitted in the frequency bandsf₂ and f₃ correspond to the third data group output from the thirdgenerator G3. Thus, even in the worst channel conditions, only the firstOFDM symbols are lost while the second and third OFDM symbols arelosslessly transmitted.

Consequently, effects are equivalent to the {fraction (1/2)}convolutional encoding so that a {fraction (1/2)} rate of errorcorrection capability is maintained though a {fraction (1/2)} rateconvolutional decoding at a reception side.

FIGS. 7A to 7D are diagrams illustrating examples of thetime-domain-extended transmission scheme applied to each of thetransmission channel patterns according to an embodiment of the presentinvention. By way of example, four kinds of the transmission channelpattern are utilized with respect to the three frequency bands f₁, f₂,f₃.

In the transmission channel CH#1={f₁, f₂, f₃, f₁, f₂, f₃, . . . } ofFIG. 7A, the frequency bands f₁ and f₂ transmit the first OFDM symbols,the frequency bands f₃ and f₁ transmit the second OFDM symbols, and thefrequency bands f₂ and f₃ transmit the third OFDM symbols in sequence.

In the transmission channel CH#2={f₁, f₃, f₂, f₁, f₃, f₂, . . . } ofFIG. 7B, the frequency bands f₁, and f₃ transmit the first OFDM symbols,the frequency bands f₂ and f₁ transmit the second OFDM symbols, and thefrequency bands f₃ and f₂ transmit the third OFDM symbols in sequence.

In the transmission channel CH#3={f₁, f₁, f₂, f₂, f₃, . . . } of FIG.7C, the frequency bands f₁, f₁, and f₂ respectively transmit the first,second, and third OFDM symbols, and the frequency bands f₂, f₃, and f₃respectively transmit the first, second, and third OFDM symbols onceagain.

In the transmission channel CH#4={f₁, f₁, f₃, f₃, f₂, f₂, . . . } ofFIG. 7D, the frequency bands f₁, f₁, and f₃ respectively transmit theflit second, and third OFDM symbols, and the frequency bands f₃, f₂, andf₂ respectively transmit the first, second, and third OFDM symbols onceagain.

In the light of the foregoing, the TFI-OFDM transmission systemaccording to an embodiment of the present invention transmits thedifferent data loaded in the positive and negative frequency domains,respectively, and transmits the OFDM symbols extended into the timedomain As a result, the data transmission rate becomes the same as theconventional TFI-OFDM transmission scheme and the effects of thecollision due to interfering signals from the adjacent SOP is mitigated

FIG. 8 is a schematic block diagram illustrating a TFI-OFDM receptionsystem according to an embodiment of the present invention. Referring toFIG. 8, the reception system includes a receiver 810, a synchronizationand channel estimation part 820, a collision detector 830, an OFDMdemodulator 840, a phase compensator 850, an equalizer 860, a datadetector 870, and a deinterleaver 880.

The receiver 810 down-converts a certain number of frequency bands intopredetermined transmission channel patterns.

The synchronization and channel estimation part 820 detects a syncsignal through cross-correlation between preambles by scanning aspecific frequency band of the certain number of the frequency bands. Achannel is estimated by using two reference OFDM symbols per onefrequency band. For example, for the transmission channel pattern {f₁,f₂, f₃, f₁, f₂, f₃ . . . }, OFDM symbols transmitted in the underlinedidentical frequency band f, are present at three OFDM-symbol intervalson the time axis. Thus, a phase difference results from a phase offset,timing offset, and frequency offset between two OFDM symbols transmittedin a single frequency band Accordingly, channels are estimated using thephase difference of two OFDM symbols.

The collision detector 830 determines collisions of OFDM symbols thatare transmitted in the multi-path channel conditions. The algorithm forthe collision determination can vary. According to an embodiment of thepresent invention, the collisions are detected by measuring the powersof the received symbols. The steps for the collision determination willfollow with reference to FIG. 9.

The OFDM demodulator 840 outputs data of the frequency domain from theOFDM symbols of the time domain that are input with the samespecification as in the transmitting end by using the fast Fouriertransform (FFT).

The phase compensator 850 compensates the phase of the received signalby utilizing a combination of a reference-based method and adecision-directed method.

The equalizer 860 removes multi-paths of the received signal bygenerally using a ONE-TAP equalizer according to the OFDM transmissioncharacteristics.

The data detector 870 detects only data to be received and processedbased on the determination of the collision detector 830. Preferably,but not necessarily, the data detector 870 detects data which correspondto non-collided OFDM symbols of the same OFDM symbols received twice.

The deinterleaver 880 deinterleaves the detected data of the datadetector 870 in the reverse order of interleaving at the transmittingend

FIG. 9 is a flowchart illustrating exemplary steps for selectivelydetecting non-collided OFDM symbols in the multi-piconet environment bythe collision detector 830 of the TFI-OFDM reception system according toan embodiment of the present invention. In the following example, thecollision is detected with respect to the OFDM symbols transmitted inthe transmission channel {f₁, f₂, f₃, f₁, f₂, f₃}.

The first OFDM symbols twitted in the frequency bands f₁ and f₂ arereceived in sequence.

The collision detector 830 measures a power R1 of the first OFDM symbols(hereafter refer to as a ‘first power’) transmitted in the currentfrequency band f₁ and a power R2 of the first OFDM symbols (hereinafterrefer to as a ‘second power’) transmitted in the next frequency band f₂.Next, an average power TH1 is calculated with respect to the OFDMsymbols previously transmitted in the frequency band f, (hereinafterreferred to as a ‘first average power’), and an average power TH2 iscalculated with respect to the OFDM symbols previously transmitted inthe frequency band f₂ (hereinafter refer to as a ‘second average power)at step S911.

The first power R1 is compared with the first average power TH1, and thesecond power R2 is compared with the second average power TH2 at stepS913. If the first power R1 is less than the sum of the first averagepower TH1 and a margin m1 and the second power R2 is less than the sumof the second average power TH2 and a margin m2, then there are nocollisions in the first OFDM symbols transmitted in the frequency bandf₁ and the first OFDM symbols transmitted in the frequency band f₂ (stepS915). Hence, the data detector 870 detects the data using both of thefirst OFDM symbols Knitted in the frequency bands f₁ and f₂ at stepS917.

If the first power R1 is greater than the sum of the first average powerTH1 and the margin m1 and the second power R2 is less than the sum ofthe second average power TH2 and the margin m2 at step S921, then thefirst OFDM symbols transmitted in the frequency band f, have collisions(step S923). Accordingly, the data detector 870 detects data by use ofthe first OFDM symbols transmitted in the frequency band f₂ at stepS925.

If the first power R1 is less than the sum of the first average powerTH1 and the margin m1 and the second power R2 is greater than the sum ofthe second average power TH2 and the margin m2 at step S931, then thefirst OFDM symbols transmitted in the frequency band f₂ have collisions(step S933). Accordingly, the data detector 870 detects data by use ofthe first OFDM symbols transmitted in the frequency band f₁ at stepS935.

If the first power R1 is greater than the sum of the first average powerTH1 and the margin m1 and the second power R2 is greater than the sum ofthe second average power TH2 and the margin m2 at step S931, then thereare collisions in both of the first OFDM symbols transmitted in thefrequency band f, and the first OFDM symbols transmitted in thefrequency band f₂ (step S941). Accordingly, the data detector 870detects data using both of the first OFDM symbols transmitted in thefrequency bands ft and f₂. Alternatively, the data detector 870 may notuse both of the first OFDM symbols (step S942).

Referring back to FIG. 3A, if the convolutional encoder 320 performsboth of the symbol interleaving and the tone interleaving, theinterleaver 330 detects data using two collided OFDM symbols. Referringback to FIG. 3B, if the convolutional encoder 321 performs the toneinterleaving alone, the interleaver 331 can correct errors through theconvolutional decoding of a ½ rate as shown in FIGS. 6B and 6C withouthaving to use the two collided OFDM symbols.

As described, the collision detection is executed with respect to thesame OFDM symbols received in sequence.

In the light of the foregoing, the reception performance is enhanced byselectively using the non-collided (OFDM symbolic in the multi-piconetenvironment for the data reception.

The TFI-OFDM transmission system according to an embodiment of thepresent invention OFDM-modulates the different data in the positive andnegative frequency domains and transmits the modulated OFDM symbols inthe time domain at least two times, to thus mitigate the collisionsresulting from the adjacent SOPs in the multi-piconet environment

The TFI-OFDM reception system according to an embodiment of the presentinvention selectively utilities the non-collided OFDM symbols for datareception in the multi-piconet environment

While the embodiments of the present invention have been described withreference to exemplary embodiments thereof, additional variations andmodifications of the embodiments may occur to those skilled in the artonce they learn of the basic inventive concepts. Therefore, it isintended that the appended claims shall be construed to include both theabove embodiments and all such variations and modifications that fallwithin the spirit and scope of the invention.

1. A time frequency interleaved-orthogonal frequency divisionmultiplexing (TFI-OFDM) transmission system for an ultra wide band (UWB)communication, comprising: a data generator generating data having arate corresponding to a transmission speed mode; a convolutional encoderconvolutional-encoding the data; an interleaver bit-interleaving theencoded data; an OFDM modulator inputting a first data group into apositive frequency domain and a second data group into a negativefrequency domain, executing a invert fast Fourier transform (IFFT), andoutputting OFDM symbols; a buffer temporarily storing the OFDM symbolsto sequentially transmit the OFDM symbols in a time domain at least twotimes; and a frequency generator generating certain frequencies totransmit the OFDM symbols in a certain number of frequency bandscorresponding to transmission channels.
 2. The transmission system ofclaim 1, wherein the convolutional encoder has a ⅓ coding rate andoutputs first, second, and third data groups which are respectivelyencoded in first second, and third generators, and wherein theinterleaver executes a tone-interleaving with respect to each of thefirst, second, and third data groups.
 3. The transmission system ofclaim 1, wherein the transmission speed mode is one of a 110 Mbps modeand a 200 Mbps mode.
 4. The transmission system of claim 1, wherein, ifthe transmission speed mode is a 55 Mbps mode, the OFDM modulator inputsthe first data group into a half (½) of the positive frequency domain, acopy of the first data group into the remaining half (½) of the positivefrequency domain, the second data group into a half (½) of the negativefrequency domain, and a copy of the second data group into the remaininghalf (½) of the negative frequency domain; and executes IFFT modulation.5. A transmission method of a time frequency interleaved-orthogonalfrequency division multiplexing (TFI-OFDM) transmission system for aultra wide band (UWB) communication, comprising: (a) generating datahaving a speed corresponding to a transmission speed mode; (b)convolutional-encoding the data; (c) bit-interleaving the encoded data;(d) inputting a first data group into a positive frequency domain and asecond data group into a negative frequency domain, executing a invertfast Fourier transform (IFFT), and outputting OFDM symbols; and (e)sequentially transmitting the OFDM symbols in different frequency bandsat least two times.
 6. The transmission method of claim 5, wherein thestep (b) encodes at a ⅓ coding rate and outputs first, second, and thirddata groups, respectively, and the step (c) executes a tone-interleavingto each of the first, second, and third data groups.
 7. The emissionmethod of claim 5, wherein the transmission speed mode is one of a 110Mbps mode and a 200 Mbps mode.
 8. The transmission method of claim 5,wherein, if the transmission speed mode is a 55 Mbps mode, the step (d)inputs the first data group into a half (½) of the positive frequencydomain, a copy of the first data group into the remaining half (½) ofthe positive frequency domain, the second data group into a half (½) ofthe negative frequency domain, and a copy of the second data group intothe remaining (½) of the negative frequency domain; and executing IFFTmodulation.
 9. A time frequency interleaved-orthogonal frequencydivision multiplexing (TFI-OFDM) reception system for a ultra wide band(UWB) communication, comprising: a receiver receiving OFDM symbolstransmitted in a certain number of frequency bands corresponding totransmission channels; a collision detector determining collisions of atleast two of the OFDM symbols by measuring powers with respect at leasttwo of the OFDM symbols sequentially received and containing the samedata; and a data detector detecting data to be processed based on thecollision which is determined with respect to the at least two of theOFDM symbols by the collision detector.
 10. The reception system ofclaim 9, wherein the collision detector measures a first and a secondpower with respect to the same OFDM symbols sequentially received from afirst frequency band and a second frequency band, measures a firstaverage power and a second average power with respect to signalsreceived from the first frequency band and the second frequency band,compares the first power and the first average power, compares thesecond power and the second average power, determines collisions in theOFDM symbols of the first frequency band and the second frequency band,and provides collision information to the data detector.
 11. Thereception system of claim 10, wherein the collision detector determinesthat the OFDM symbols of both of the first frequency band and the secondfrequency band do not have collisions if the first power is less than asum of the first average power and a first margin and the second poweris less than a sum of the second average power and a second margin, andthe data detector detects data corresponding to the OFDM symbols of thefirst frequency band and the second frequency band.
 12. The receptionsystem of claim 10, wherein the collision detector determines that theOFDM symbols of the second frequency band have collisions if the firstpower is less than a sun of the first average power and a first marginand the second power is greater than a sum of the second average powerand a second margin, and the data detector detects data corresponding tothe OFDM symbols of the first frequency band.
 13. The reception systemof claim 10, wherein the collision detector determines that the OFDMsymbols of the first frequency band have collisions if the first poweris greater than a sum of the first average power and a first margin andthe second power is less than a sum of the second average power and asecond margin, and the data detector detects data corresponding to theOFDM symbols of the second frequency band.
 14. The reception system ofclaim 10, wherein the collision detector determines that the OFDMsymbols of both of the first frequency band and the second frequencyband have collisions if the first power is greater than a sum of thefirst average power and a first margin and the second power is greaterthan a sum of the second average power and a second margin, and the datadetector detects data corresponding to the OFDM symbols of the firstfrequency band and the second frequency band.
 15. The reception systemof claim 10, wherein the collision detector determines that the OFDMsymbols of both of the fist frequency band and the second frequency bandhave collisions if the first power is greater than a sum of the firstaverage power and a first margin and the second power is greater than asum of the second average power and a second margin, and the datadetector does not detect data corresponding to the OFDM symbols of bothof the first frequency band and the second frequency band.
 16. Areception method of a time frequency interleaved-orthogonal frequencydivision multiplexing (TFI-OFDM) reception system for an ultra wide band(UWB) communication, comprising: (a) receiving OFDM symbols transmittedin a certain number of frequency bands corresponding to transmissionchannels; (b) determining collisions in at least two of the OFDM symbolsby measuring powers with respect to the at least two OFDM symbolssequentially received and containing the same data; and (c) detectingdata to be processed from the at least two of the OFDM symbols based onthe collision determination.
 17. The reception method of claim 16,wherein the step (b) comprises: (b-1) measuring a first power and asecond power with respect to the same OFDM symbols sequentially receivedfrom a first frequency band and a second frequency band; (b-2) measuringa first average power and a second average power with respect to eachsignal received from the first frequency band and the second frequencyband; and (b-3) comparing the first power and the first average power,comparing the second power and the second average power, determiningcollisions in the OFDM symbols of the first frequency band and thesecond frequency band, and providing the collision determination to thestep (c).
 18. The reception method of claim 17, wherein the step (b-3)determines that the OFDM symbols of both of the first frequency band andthe second frequency band do not have collisions if the first power isless than a sum of the first average power and a first margin and thesecond power is less than a sum of the second average power and a secondmargin, and the step (c) detects data corresponding to the OFDM symbolsof the first frequency band and second frequency band.
 19. The receptionmethod of claim 17, wherein the step (b3) determines that the OFDMsymbols of the second frequency band have collisions if the first poweris less than a sum of the first average power and a first margin and thesecond power is greater than a sum of the second average power and asecond margin, and the step (c) detects data corresponding to the OFDMsymbols of the first frequency band.
 20. The reception method of claim17, wherein the step (b3) determines that the OFDM symbols of the firstfrequency band have collisions if the first power is greater than a sumof the first average power and a first margin and the second power isless than a sum of the second average power and a second margin, and thestep (c) detects data corresponding to the OFDM symbols of the secondfrequency band.
 21. The reception method of claim 17, wherein the step(b-3) determines that the OFDM symbols of both of the first frequencyband and the second frequency band have collisions if the first power isgreater than a sum of the first average power and a first mat and thesecond power is greater than a sum of the second average power and asecond margin, and the step (c) detects data corresponding to the OFDMsymbols of the first frequency band and the second frequency band. 22.The reception method of claim 17, wherein the step (b-3) determines thatOFDM symbols of both of the first frequency band and the secondfrequency band have collisions if the first power is greater than a sumof the first average power and a first margin and the second power isgreater than a sum of the second average power and a second margin, andthe step (c) does not detect data corresponding to the OFDM symbols ofboth of the first frequency band and the second frequency band.